System and method for service independent data routing

ABSTRACT

Data are rerouted over a network having a uniform-capacity Tandem Connection by detecting a failure in a link in a path, maintaining the path through a Tandem Connection that does not include the failed link, and rerouting the data through the Tandem Connection based on information embedded in a tandem layer in the data, and independent of the constituent payload capacities within the tandem connection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/311,214filed May, 13, 1999, now U.S. Pat. No. 6,757,243 which claimed thebenefit of U.S. Provisional Patent Application Ser. No. 60/114,148entitled “A System and Method for Service Independent Data Routing” andfiled Dec. 29, 1998.

TECHNICAL FIELD

The present invention relates to communications on a network. Inparticular, the present invention relates to routing data along aSynchronous Optical Network.

BACKGROUND

Present-day optical data transport networks have high capacity and arevery flexible in terms of allowing for different payload types and datarates. The combination of high capacity and high flexibility, however,gives rise to routing problems if data, for whatever reason, requiresrerouting from its original path along the network. Specifically,because optical networks can carry large amounts of data at variousspeeds and sizes, present methods of rerouting are incapable of quicklyand efficiently rerouting this data.

Within the field of optical networking, various standards exist forinterfacing optical telephone networks. In North America, the SONET(Synchronous Optical Network) standards are used, while in Europe andmost of Asia, the SDH (Synchronous Digital Hierarchy) standards areused. The SONET standards, and their SDH analogs, are used forinterfacing equipment from different vendors. The SONET and SDHstandards are similar; and for the purposes of this document, the termSONET includes both the SONET and SDH standards.

Several advantages are derived from using SONET. One advantage is thatproprietary protocols for fiber-based digital transport have essentiallybeen eliminated. SONET is based on the principle of direct synchronousmultiplexing, which allows separate, slower signals to be multiplexeddirectly onto higher speed SONET signals without intermediate stages ofmultiplexing. Additionally, SONET provides advanced network managementfeatures, using nearly 5% of the total bandwidth. The SONET protocol isdescribed in American National Standard for Telecommunications—DigitalHierarchy—Optical interface rates and formats specifications (SONET),ANSI T1.105-1991, which is hereby incorporated by reference.

A SONET protocol stack consists of the following four layers: thephotonic layer, the section layer, the line layer, and the path layer.The photonic layer relates to converting electrical signals to opticalsignals. The section layer relates to the transport of STS-n(Synchronous Transport Signal) frames across the physical medium.Functions include framing, scrambling, section-error monitoring andcommunicating and adding the section-layer overhead.

The line layer allows the path layer payload to be transported, and itprovides synchronization and multiplexing for the path layer. A line isthe medium required to transmit data from the originating equipment tothe terminating equipment. Finally, the path layer deals with thetransport and mapping of services between path terminating equipment.These services include, but are not limited to, DS1, DS3 and video. Thepath layer carries information for mapping these services into an STSframe.

Providing end-to-end service requires fast service provisioning,maintenance, and quality assurance. The layered architecture in SONEThelps a network operator to achieve service objectives for all servicepaths originating and terminating within the service provider's networkdomain. Some SONET signals, however, originate and terminate outside anetwork operator's domain. The network operators do not have access tothe path-terminating points for such service signal. Thus, to meetend-to-end service objectives to manage all paths within the interfaceoriginating from all inter-network paths, an optional intermediate layercalled Tandem Connection Overhead has been defined in the standards.This optional Tandem Connection Overhead layer exists between the linelayer and the path layer, and is a standard specified in AmericanNational Standard for Telecommunications—Synchronous Optical Network(SONET) Tandem Connection Maintenance, ANSI T1.105.05-1994, herebyincorporated by reference. As discussed in the standard, the TandemConnection Overhead layer deals with the reliable transport ofpath-layer payload and its overhead across a network. The use of TandemConnection is application specific and at the discretion of the carrier.

A Tandem Connection is defined in the standard as a group of N STS-1s (Nis any of the allowed line rate values) that are transported andmaintained together through one or more tandem line systems, with theconstituent SPE (Synchronous Payload Envelope) payload capacitiesunaltered. Tandem Connection maintenance can be performed in a singleSTS-1 (where STS is the digital version of the OC standard) or on abundle with a capacity of N STS-1s, where N is any of the allowed linerate values. The size of bundles supported is application-specific anddepends on the equipment used.

Before SONET was used, Plesiochronous Digital Hierarchy (PDH) networksexisted with their own type of multiplexing. The types of multiplexingperformed, however, placed severe restrictions on how a high-capacitypipe could be used to transport a variety of lower order digital pipes.In the pre-SONET world (including PDH), there was only one type ofsignal: the DS3 signal at 45 Mbit per second. In this signal, there isno standard overhead frame. Thus, if there is a failure in the network,only one type of signal with one type of payload at one type of rateneeds to be multiplexed and sorted. If, however, a variety of signals,payloads and rates exist in a SONET environment, this multiplexing andsorting is extremely difficult, and can make it very difficult toreroute data in a practical way. In this scheme, if there is a networkfailure, rerouting and recreating the data is extremely difficultbecause within a few milliseconds, the system must figure out the slotsneeded for alternate routes, and then must assign those slots foralternate payloads.

It is clear from the above discussion that the desirable characteristicsof high capacity and flexibility provided by optical networks createsefficiency problems if data on an optical network need to be rerouted.

SUMMARY OF THE INVENTION

To alleviate the problems inherent in the prior art, a system and methodare introduced to route data along an optical network independent ofpayload type. Because the routing is performed independently of payloadtype, the routing is deemed service independent.

In one embodiment of the present invention, a network failure isdetected on a path between a first point and a second point. Analternate path on the network is established from the first point to thesecond point, the alternate path comprising a uniform-capacity tandemcircuit. The data are then rerouted through the alternate path based oninformation embedded in a tandem layer in the data, and independent ofthe constituent payload capacities within the tandem connection.

For the purposes of the present invention, the following definitions areused: A link is a physical connection between any connected nodes; apath is the physical portion of a network between, and defined by, astart point and an end point; and a path can traverse over multiplelinks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system overview of an embodiment of the present inventionfeaturing a network made up of various Tandem Connection paths betweenvarious points.

FIG. 2 is a flow chart of a method of routing data over a network havinga uniform-capacity Tandem Connection, according to an embodiment of thepresent invention.

FIG. 3 is a block diagram of an apparatus for routing data over anetwork having a uniform-capacity Tandem Connection, according to anembodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to routing data over a network. Inparticular, the present invention relates to using characteristics ofSONET to route data along a network.

Where data rerouting is required on an optical network, the complexityand large amount of payload types possible make it extremely difficultto reroute each payload individually. More specifically, as discussedabove, fiber-optic networks have the ability to carry a variety ofpayload types at a variety of data rates, and this ability makes payloadrerouting very difficult.

For example, assume a link exists with an OC-48 bandwidth. On this OC-48link can exist different types of payload bandwidth such as a singleSTS-1, or 3 STS-1s that are combined into a single payload like STS12-C. In other words, the OC-48 link can carry a mixture of payloads; soif the link fails, the different bandwidth payloads also fail. To remedythis, instead of searching for these different bandwidths in analternate route, the present invention provides for maintaining ahomogeneous bandwidth that encompasses all the other bandwidths. Inother words, a uniform bandwidth is created that will accept anylower-rate bandwidth.

The present invention uses aspects of SONET technology to develop aservice-independent transport network that can be provisioned, managed,and restored in ways that are independent of payload types in the SONETsignals. In a SONET environment, a cross connect can accept data streamsfrom a variety of tributaries, and the data streams can be multiplexedtogether. Based on this aspect of SONET, in the event of a failure in anetwork link, the individual payloads need not be individually rerouted;rather, embodiments of the present invention are based on therecognition that a number of payloads can be bundled together into onelogical bundle defined by data in the Tandem Connection overhead of aTandem Connection, and that one logical bundle can be rerouted as such,independent of its constituent payloads. That is, Tandem Connectionallows a network to combine various types of payloads into a logicalbundle; and once this is done, if there is a fiber cut, each bundle canbe rerouted as a complete bundle from one digital cross connect toanother, such as from DCS 101 to DCS 102 in FIG. 1, rather thanindividually rerouting each payload. The Tandem Connection standardprovides a map of where the bundle begins, where the bundle ends, andwhat is in the bundle. The invention takes advantage of that standard tomake routing, or rerouting, decisions on the basis of these bundles.

A Tandem Connection can be defined for a single STS payload, or for abundle of STS payloads, to provide network-level management functionsbetween two path-terminating points. These functions include signalquality, Tandem Connection trace for signal verification, idle signalidentification, and testing using test-signal and far-end performance.The Tandem Connection is managed as a single entity between the TandemConnection terminating points, regardless of the number of STS pathswithin the Tandem Connection. To do this, a Tandem Connection can usethe Z5 path-overhead byte of the first STS path containing the Z5path-overhead byte for the Tandem Connection layer functions. The firstfour bits of the Z5 byte are used to calculate the bit-error countwithin the Tandem Connection. The last four bits are typically used fora datalink between the Tandem Connection terminating points. Thedatalink carries Tandem Connection maintenance messages, trace, idlesignal identification, test-signal identification and far-endperformance messages. Because a Tandem Connection cannot change anypath-overhead byte, any alterations to the path overhead that are madeat the entry point of the Tandem Connection are reconstructed at theTandem Connection exit point. Thus, the Tandem Connection is transparentto the path overhead. It is this feature that allows a Tandem Connectionto provide service-independent, or payload-independent, transport. Onceindividual payloads are assigned the appropriate path layer, they can berouted through the Tandem Connection as one logical bundle.

Tandem Connection allows for end-to-end network performance management,and allows monitoring of signal integrity within a SONET network. Inaddition, the Tandem Connection creates a data link between definedendpoints. In particular, Tandem Connection allows a SONET network totreat a variety of incoming data as a single logical entity. When aTandem Connection is created between two points, the payloads must beprovisioned. That is, each payload, or set of payloads, is determined tobelong to a specific Tandem Connection. Thus, where a Tandem Connectionis employed that relates to multiple payloads between two points, thereis already, in essence, a sense of a relationship between those payloadsin that particular Tandem Connection. It is this property that allowsthe Tandem Connection to be used for the new use of transmissionrestoration.

Having recognized that the individual payloads are associated with oneanother, i.e., are bundled together, the bundle can be rerouted as asingle unit if a link fails. In one embodiment of the present invention,idle bandwidth capacity exists on the Tandem Connection such that thebundled payloads can be provisioned into this idle capacity. Thererouting can be performed in any way known in the art.

Note that the link capacity is divided into predetermined bandwidths, ormultiples of a bandwidth. In other words, the bandwidth available over alink is divided up into slots that are associated with a given uniformbandwidth. For example, assume a link exists that is in 48 units ofDS-3. Within those 48 units, the data itself can consist of, possiblyone 48^(th), one 16^(th), one 12^(th), etc. In the present invention,one fraction of these 48 units can be chosen as the uniform unit for theTandem Connection. Thus, if one-fourth of the 48 units are chosen as theuniform unit for the Tandem Connection, payloads that require any slotsize up to one fourth of the overall 48 units can be rerouted accordingto the present invention. In this example, multiple payloads can bererouted along this chosen slot as long as the total bandwidth of thepayloads do not exceed the one-fourth unit. Of course, each link canhave, as its bandwidth unit, a different bandwidth unit from anotherlink.

As an overview of an embodiment of the present invention, assume thereexists an optical network that can carry a variety of payloads betweentwo points along a variety of links on the network. For example, in FIG.1, for data to travel from digital cross connect system (DCS) 101 to DCS102, the data can travel along path A-B by traveling along link A-B, orthe data can travel along path A-B by traveling along link D-A to linkC-D to link B-C and finally to DCS 102. Assume, for the purpose of thisexample, that the data is being routed from DCS 101 to DCS 102 alonglink A-B until that path is somehow disrupted. The data can be reroutedfrom DCS 101 to DCS 102 along path A-B-C-D defined by links that avoidthe failed links. Of course, as discussed above, if the path were to bedisrupted under the PDH standard discussed in the background, thenetwork would need to reroute the data according to its payload. Becausethis is an optical network carrying a variety of payloads, thisrerouting task is extremely cumbersome. Using an embodiment of thepresent invention, however, multiple payloads can be rerouted as asingle logical unit.

As another example, assume that the network consists of a fiber thatcarries live traffic. This fiber includes both unused channels andchannels used to carry traffic. Now assume that on the network there arefour DCS's, or nodes, and that between each of these nodes there is anoptical link that carries traffic at, for example, an OC 48 bandwidth(i.e., line rate) (which is equivalent to 48 DS 3s in flow-throughcapacity). The OC 48 bandwidth can be divided into 4 sets of 12 slots,each set with 12 DS 3 flow-through capacity. Each of these 4 sets of 12slots can be defined to be a Tandem Connection; thus, the OC 48bandwidth is divided into 4 Tandem Connections. Using FIG. 1, assumethat the network is an OC-48 network. DCS 101 and DCS 102 can be giveninstructions to maintain 4 bandwidth units of 12 slots each. Thus, whena number of payloads need to be delivered along path A-B, these payloadunits can be combined into a single logical bundle and be rerouted alongthe active links, provided the bandwidth needs of the bundled payloadsdo not exceed 12 slots.

To divide the OC 48 bandwidth into the 4 sets of 12 slots, in thisexample using FIG. 1, DCS 102 can be sent instructions indicating thatthe first 12 DS-3 slot numbers 1-12 in the OC-48 line belong to aspecific Tandem Connection. To do this, a logic element can residewithin DCS 102, for example, and this logic element understands that aTandem Connection exists between DCS 101 and DCS 102. The TandemConnection can then be managed using datalink channels in the pathoverhead. If a Tandem Connection is set up between DCS 101, 104, 103 and102, these Tandem Connections can be used as standby connections in caseof a failure.

To establish a Tandem Connection, an operator at the element managementsystem (EMS) or network management system (NMS) can issue commands to aDCS that tells the DCS to set up a Tandem Connection at the interfaceport of the DCS. The DCS then establishes the Tandem Connection and inits memory keeps the record of the created Tandem Connection. The portand the DCS control system (that resides within the DCS and controls andmanages functions within the DCS) then take other actions necessary formaintaining the Tandem Connection such as performance checking of theTandem Connection, Tandem Connection ID, etc.

To reroute, the DCS acts analogously to a conventionaltelecommunications switch. Thus, when a DCS receives commands fromoutside agents such as an EMS or NMS, or when the DCS's own controlsystem decides that a path must be changed, the DCS determines analternate route and then directs data accordingly. Because TandemConnections are used, data can be rerouted independent of payload. Thatis, using the Tandem Connection overhead, any combination of payloadscan be combined and treated as a large entity that contains all theoriginal entities that are rerouted.

In the above example, a homogenous network is created by treating one ofthe four slots as a network with a uniform Tandem Connection capacity of12 STS-1s. Note that the same principle can be applied to create anetwork with Tandem Connections of higher rates. For example, one cancreate a Tandem Connection with a capacity of 48 STS-1s.

As an additional example, in a large network, a subset of nodes can beconnected with only OC-48 or OC-192 links to form a high-capacitybackbone network. The high-capacity backbone network can then be managedand restored at, for example, the OC-48 level with Tandem Connections of48 STS-1s capacity. Additionally, within this same physical network, twoindependent virtual layers of networks can be created. One of the layerscan be a Tandem Connection with 12 STS-1s capacity, and the other layercan be a Tandem Connection with 48 STS-1s capacity. Depending on theultimate capacity of a network, a variety of layers of TandemConnections can be established on the network with a variety ofbandwidths.

FIG. 2 is a flow chart of a method of practicing the present invention.The steps of the flow chart are not intended to imply a necessary orderto the steps; the steps of the method can be implemented in any waypracticable. At step 201, a failure is detected in a path between afirst point and a second point on the network. At step 202, an alternatepath is established between the first point and the second point. Inthis invention, the alternate path is a uniform-capacity tandem circuit.For example, the alternate path can be a Tandem Connection Circuit witha flow-through capacity of some multiple of DS n capacities. In fact,the flow-through capacity can have the capacity of any multiple of anydigital service signal speed. This alternate path can be a series oflinks connected end to end, each link being a Tandem Connection link;alternatively, the alternate path can be a single Tandem Connectioncircuit.

At step 203, the data are rerouted through the alternate path based oninformation embedded in the tandem layer. Because the data are reroutedbased on information embedded in the tandem layer, the rerouting can beperformed independently of the constituent payload within the TandemConnection circuit.

The rerouting can be performed in a variety of ways. In one embodimentof the present invention, a central control system that monitors some orall of the DCS nodes on the network can detect if there is a networkfailure between two or more of the nodes. If a failure is detected, thecentral control system takes advantage of the idle capacity of each ofthe nodes by sending the nodes instructions to reestablish theconnection between the endpoints of the original path. In anotherembodiment of the present invention, the nodes can have the capabilityof communicating with one another. If a node detects a network failurebetween two or more nodes, the node informs the other nodes that datamust be rerouted along an alternate path. The nodes themselves cancreate the alternate path by using the datalink channel embedded in theTandem Connection layer to create Tandem Connection cross connects.

FIG. 3 is a block diagram of an apparatus embodiment of the presentinvention. Processor 301 is coupled to memory 302 and port 303. Memory302 stores instructions adapted to be executed by processor 301 toperform a method embodiment of the present invention. For example,memory 302 stores instructions adapted to be executed by processor 301to detect a failure in a network between a first point and a secondpoint along a circuit; establish an alternate circuit from the firstpoint to the second point, the alternate circuit comprising auniform-capacity tandem circuit; and reroute the data through thealternate circuit, based on information embedded in a tandem layer, andindependent of the constituent payload capacities within the tandemconnection. The apparatus can reside at a DCS or a central controlsystem.

For the purposes of this application, memory includes any medium capableof storing instructions adapted to be executed by a processor. Someexamples of such media include, but are not limited to, RAM, ROM, floppydisks, CDROM, magnetic tape, hard drives, optical storage units, and anyother device that can store digital information. In one embodiment, theinstructions are stored on the medium in a compressed and/or encryptedformat. As used herein, the phrase “adapted to be executed by aprocessor” is meant to encompass instructions stored in a compressedand/or encrypted format, as well as instructions that have to becompiled or installed by an installer before being executed by theprocessor.

The present invention has been described in terms of several embodimentssolely for the purpose of illustration. Persons skilled in the art willrecognize from this description that the invention is not limited to theembodiments described, but may be practiced with modifications andalterations limited only by the spirit and scope of the appended claims.

1. A method for use in a network in which a plurality of payloads are initially carried on a link of a path in accordance with a predetermined protocol, the method comprising: utilizing a tandem connection layer of said protocol, in response to a failure in said link, to combine and manage said payloads as a single logical entity on at least one other link independent of the different payload capacities of said plurality of payloads and without individually rerouting each payload, the management of said single logical entity being based on information embedded in the tandem connection layer of the protocol.
 2. An apparatus for routing data over a network in which a plurality of payloads are routed on a link in a path in accordance with a predetermined protocol, the apparatus comprising: (a) a processor, (b) a port; and (c) a memory coupled to said port and said processor, said memory storing instructions adapted to be executed by said processor to utilize a tandem connection layer of said protocol, in response to a failure of said link, to combine and manage said payloads as a single logical entity on at least one other link independent of the different payload capacities of said plurality of payloads and without individually rerouting each payload, the management of said single logical entity being based on information embedded in the tandem connection layer of the protocol.
 3. A method for use in a SONET network comprising at least first, second and third cross-connects, the method comprising establishing a SONET tandem connection over a set of links from said first cross-connect to said second cross-connect via said third cross-connect, said SONET tandem connection being in conformance with ANSI standard T1.105.05; routing one or more payloads between said first and second cross-connects over another link; and responsive to a failure of said another link, combining and rerouting said payloads over said set of links as a single logical entity utilizing said SONET tandem connection and without individually rerouting each payload, management of said single logical entity being based on the Z5 path overhead byte of at least one of said payloads, said combining and said management being performed independent of the different payload capacities of said payloads. 